Evidence: The Gathering

[Mudhammam]

Who bothers to write a contemporaneous biography about someone who hasn't achieved anything yet?

What do you mean? 

Are the Gospels any different? Did Luke interview Mary, for example, to get the background story about the Annunciation from her?

Yes, the Gospels are clearly different from the examples you cite. They were composed largely for the purpose of conveying theological and ethical guidance to a particular sect of Christians. They make no attempt at establishing historical credibility because that's not their concern. Their aim is rather to interpret the events of Jesus life, using embellishment and by allegorizng the Old Testament in conjunction with Greek philosophy, to create a portrait of reality as they perceive it - one that is highly superstitious and therefore, almost completely fiction, one that includes the belief in evil spirits which roam the earth and are the cause of all falsehood and idolatry. They're stories, written by authors whose backgrounds are unknown until many decades later when church authorities who wished to legitimize their dogmas by establishing the notion of apostolic succession attached specific names to the works that supported their point of view. 

But why would we expect there to be much written about Jesus in a largely illiterate age when even more famous people got scant mention in the ancient histories? Even Pontius Pilate was long-thought to be a mythical figure until an inscription bearing his name was finally discovered on a stone tablet a few years ago.

Well, most of ancient history is lost because for 1,000 years the church preserved what it felt were in its interests and either destroyed what it feared, or suppressed it. So, it's not shocking that the information we have about Pilate, apart from Philo of Alexandria, consists of nonsense like The Acts of Pilate.

You say that my objections can be easily overcome - but bear in mind it's not me you and your fellow religionists need to convince. It's the majority of historians.